Ms Sturgeon confirmed that EU membership remained SNP policy but hinted at the EFTA “transition” plan when she told ITV’s Peston on Sunday programme that single market membership was the “minimum” benchmark for Scotland.

Mr Salmond went further by telling BBC Radio Five Live’s Pienaar's Politics programme that there was a difference between “what you do as a transition and what you would do as your aim.”

Confirming he was referring to the Norway model, he said: “The idea is to have continuous membership of the European Economic Area. That’s the logic behind Nicola Sturgeon’s 18 months to two years for the referendum.

“By definition, that is a lot easier to achieve very, very quickly because EFTA is an organisation of four countries. The European Commission in a number of examples has negotiated arrangements like this before for accession countries.

“It’s not something that has anything like the difficulties of securing full European Union membership.”